1. Field of the Invention
The invention relates to a friction disc clutch of variable capacity for delivering torque from an engine to a geared transmission.
2. Background Art
The invention relates generally to a friction disc clutch for transferring torque from a torque source to a driven member. The clutch is adapted specifically to be used in a powertrain for an automotive vehicle to deliver torque from an engine to the torque input side of a power transmission mechanism as driving torque is delivered through the powertrain to the traction wheels. A typical friction clutch mechanism in an automotive vehicle driveline may be seen by referring to prior art U.S. Pat. Nos. 4,425,991 5,499,704, and 6,098,772.
An automotive friction clutch of this type comprises a thrust plate carried by a clutch housing in proximity to the facing of a flywheel. In the case of a powertrain having an internal combustion engine, the crankshaft of the engine would be secured to the flywheel and a friction disc assembly would be situated between the thrust plate and a radial face of the flywheel. A prior art construction of this kind is illustrated in FIGS. 1-6.
When a conventional friction clutch is used in an automotive vehicle powertrain, friction surfaces will be subject to wear and coefficients of friction will change. These factors, as well as other design characteristics, affect the operating torque capacity of the clutch. The torque capacity that is preset at the time of manufacture, however, cannot be changed within the field of service without removal of the clutch and redesigning or retrofitting its components. This is a costly and time-consuming process that is particularly undesirable in the automotive high-performance and racing clutch industry.
It is an objective of the invention to provide an improved clutch design wherein users of the clutch assembly can quickly and easily adjust the clutch spring pressure, and therefore the torque capacity of the clutch, as needed to suit a particular application or a particular operating condition. This objective is achieved by including in the clutch design one or more counteracting compression springs, which hereinafter will be referred to as pressure balance springs. The force of the pressure balance springs will partially cancel some of the force generated by a primary diaphragm spring.
The pressure balance spring can be any combination of small compression coil springs, flat springs, or stacked conical washer-type springs. They typically have a linear pressure curve; i.e., they will continuously increase in pressure linearly until their maximum compression distance is reached. A diaphragm spring also can serve as a pressure balance spring. In that case, both the primary diaphragm spring and the secondary pressure balance spring diaphragm have a bell shape pressure curve. The primary diaphragm spring and the secondary diaphragm spring, as in the case of a design with pressure balance springs with linear pressure curves, have forces that counteract each other.
The clamping force achieved by the clutch construction of the present invention is defined as the amount of force generated by the primary diaphragm spring times the mechanical spring lever ratio minus the counteracting force generated by the pressure balance springs.
The clutch design of the invention includes a rotary counter-thrust plate connected drivably to a torque source, such as a vehicle engine. A clutch assembly cover is connected to the counter-thrust plate. It defines with the counter-thrust plate a clutch housing. In a typical vehicle driveline environment, the counter-thrust plate is the engine flywheel.
A thrust plate in the clutch housing is drivably connected to the housing whereby rotary motion of the thrust plate relative to the flywheel is prevented while accommodating relative axial movement of the thrust plate.
A friction clutch disc with friction material on its peripheral portion is located between the flywheel and the thrust plate. A diaphragm spring lever in the clutch housing applies a clutch engaging force on the thrust plate. The spring lever is fulcrumed on the housing.
Pressure balance springs disposed between the thrust plate and the clutch housing oppose the clutch engaging force of the spring lever. The effective spring force of the pressure balance springs can be adjusted to effect control of the clutch torque capacity as the operating torque requirements change.
The pressure balance springs will provide also for a clutch disengagement assist, especially at high rotational speeds. This will avoid a tendency for the thrust plate to xe2x80x9cbouncexe2x80x9d or vibrate between the diaphragm spring and the clutch disc during disengagement.
Another function of the pressure balance springs is the enhancement of the quality of the clutch engagement. By tailoring the effective balance spring forces, the engagement of the clutch can be cushioned. Clutch engagement inertia forces due to rapid engagement are reduced or avoided.